The present invention relates to a method and apparatus for measuring the tension of an advancing yarn which is subject to periodic interruptions in its advance, and which is characterized by the ability to correct for any errors in the zero point output signal of the tension sensor.
German patent 24 12 153 and the corresponding U.S. Pat. No. 3,931,938, disclose a yarn winding process wherein the yarn tension is periodically detected by a sensor located at the edge of the area covered by the traverse motion of the yarn. The output of the sensor is compared with a preset desired value, and the difference is fed into a controller which acts upon a regulator for varying the speed of rotation of the winding spindle, thereby keeping the yarn tension at the desired value throughout the winding operation.
The above described winding process results in the periodic release of the sensor, and upon such release, the sensor should deliver a zero signal. However, because of heat, wear, or other possible factors, the sensor does not always return to a zero signal, and the signal may in fact drift from zero. Thus the above described method and apparatus is not suitable for continuously obtaining the absolute value of the yarn tension when the tension is periodically interrupted.
It is accordingly an object of the present invention to provide a method and apparatus for measuring the tension of an advancing yarn in a process which is subject to interruptions in the yarn path, resulting for example from the severance of the yarn, and wherein the measured signal is not falsified by errors in the zero point reading, and wherein it is possible to recognize errors of the measuring system which lead to the falsification of the measuring signals.